Directional drilling has become a standard drilling procedure whereby formations located significant lateral distances from surface wells are targeted by drilling to a depth and then also laterally. A mud motor, powered by the pressurized drilling mud injected into the drill string at the surface, is located downhole adjacent to the bit and rotates the bit to advance the bore hole. Unlike conventional drilling, in lateral directional drilling operations the drill string itself does not rotate, but rather just the bit powered by the mud motor.
During the lateral phase of directional drilling operations, a sizable portion of the drill string is in direct contact with the borehole. This causes significant frictional resistance, particularly when the drill string is not rotating. Further, when drilling operations are halted, the drill string tends to sink into mud in the bore hole, sticking and making it difficult to advance the drill string into the bore hole when drilling operations are recommenced. Overcoming the friction between the borehole and the drill string can greatly impede the ability of the driller to provide the optimal amount of weight to the drill bit to achieve the maximum penetrative rate. Frequently, the application of force to overcome the friction results in excessive weight being placed on the bit which can damage the downhole drilling equipment and reduce penetrative efficiency.
What is required is an apparatus and method of agitating or vibrating the drill string to overcome the friction arising between the drill string and the bore hole in the lateral section of directionally drilled well bore. The apparatus needs to be robust, relatively simple and capable of being inserted into the downhole environment. Such apparatus and method needs to mitigate the frictional problems of directional drilling and will preferably facilitate greater rates of penetration.
It is well known in the art to create pressure pulses in the drilling fluid for the purpose of telemetric tracking of the drill bit and the associated drill string to accurately track lateral drilling progress. However, the use of a pressure pulse to vibrate the drill string to overcome frictional resistance during directional drilling is relatively unknown.